The physical principles of a vibration damper are known in principle. Vibration dampers must be matched to the frequency of the component to be damped. The matching of the damper frequency can be achieved on the one hand by the change in the stiffness of the spring elements employed, on the other hand by a change in the damper mass. Limits are naturally imposed on the change in the damper mass of a certain system to be damped, and a change in the damper mass is therefore hardly used in practice. This leaves the variation in the spring stiffness.
On use of elastic materials in modern dampers, however, this is in principle dependent on the temperature. A spring stiffness set at a certain temperature and matched to the system to be damped changes with the ambient temperatures. Whereas this effect is often negligible in the case of structures to be damped in buildings, it plays a not inconsiderable role in the case of outdoor structures, such as, for example, in the case of wind turbines. Wind turbines are usually subjected to large temperature variations between −20° and +50° C. at which they are still operated, depending on the location. The spring stiffness of the damping parts employed and thus the excitation frequency of the system consequently changes, meaning that optimum damping or no damping at all of vibrations which occur in the structure can take place without re-adjustment of the spring stiffness of the damping parts being necessary. However, this is complex and thus expensive, if possible at all.
It is therefore an aim to employ dampers which only react insignificantly, or not at all, to changes in temperature with a change in the pre-set damper frequency.
DE 2342370 describes a hydrostatic compression spring based on a precompressed elastomer which fills a chamber and is connected in series before a second elastic spring (chamber), where the volume of the second elastic spring is significantly smaller than the elastomer which experiences the actual push deformation. The two elastomeric chambers are not connected directly. The operating behaviour of the entire compression spring is substantially the same at different temperatures due to this design.
EP 0562 161 describes vibration dampers comprising a damper mass which is arranged in a movable manner on a spring element comprising elastomeric material and which can be set in motion with a phase shift to vibrations introduced as a consequence of operation, where the spring element is fixed on a part generating the vibrations. A supplementary spring connected in parallel whose spring stiffness can be changed by aids based on mechanical movement processes is assigned to the spring element for compensation of temperature influences.
EP 2 284 416 solves the problem of temperature change by the actual elastic damping element having an electronically controllable heating element which is controlled in accordance with the ambient temperatures.
The temperature-independent damper systems described in the prior art are in some cases quite complicated, on the other hand they only work optimally in certain limited temperature ranges. Owing to the dimensions of wind turbines and the considerable temperature differences during operation, these proposed damper systems are of only limited suitability.
These also include the concepts of the dampers which are described, for example, in EP 1 286 076 A1 and EP 1 693 593 B1. EP 1 286 076 discloses a linear vibration damper whose spring/mass system is composed of the actual functional parts in or on which damping takes place, and the damper mass. The damper is set in advance via the functional part, usually before or immediately after installation into the system to be damped, so that the damper mass vibrates close to the excitation frequency with the opposite phase. The damper is thus permanently tuned to a certain excitation frequency. This setting is carried out by means of tensioning devices via the functional part. In this case, the rubber layer within the functional part is pretensioned. A reduction in the rubber pretensioning force causes a reduction in the damper frequency; an increase in the rubber pretensioning within the functional part results in a higher damper frequency. The functional parts have conical or spherical surfaces which are provided with elastomer material and form a certain angle with the longitudinal axis of the damper. EP 1 693 593 describes an adjustable three-axis damper which is based on the same principle, but comprises a multiplicity of correspondingly shaped and arranged functional parts of this type.
This rubber pretensioning in the prior-art dampers described and in other prior-art dampers is, however, dependent on the rubber temperature and/or the ambient temperature. Thus, the damper frequency changes in the case of temperature variations. This results in a damper only being able to act optimally at the temperature at which it was also set. Deviations of as little as 10° C. here can result in complete functional failure of the damper. This phenomenon is dependent on the rubber used, but is always present independently thereof. The use of dampers in accordance with the above functional principle thus requires constant ambient temperatures. However, precisely this fact is not given in most application cases. In the case of most outdoor applications, a damper must act in a large temperature range (about −20° C. to +50° C.). This is not possible with the current state of the art. For this reason, it makes sense to develop a damper which maintains its set inherent frequency over a broad temperature spectrum.